Wind energy has been used in different parts of the world for centuries to pump underground water and mill grain. Simple vertical-axis wind machines were in existence in Pursia several hundred years before the time of Christ. In the 12th century, the horizontal-axis windmills made their appearance almost simultaneously in France, England, and the Netherland.
Dutch settlers brought the windmill to the United States in the middle of the 18th century. Many windmills were built and used to pump water and grind grain.
The first machine to generate electricity from wind was designed and built in Denmark in 1890. Subsequently, several hundred machines were built in that country.
In the United States, wind machines were widely used to generate electricity in rural areas until the 1930's when the Rural Electrification Act provided farmers with cheap electricity.
In 1931, generating electricity from wind took a big step forward when a relatively large windmill of 100-kilowatt capacity was built in Russia.
In the United States, an American engineer and inventor, Palmer C. Putnam started the design of a 1,250-kilowatt wind machine in 1934. The machine was built in 1941 on a hill called Grandpa's Knob in the state of Vermont. After testing, the windmill was connected to the Central Vermont Public Service Corporation. Shortly after operation, a main bearing and a blade failed. Because of World War II, the project was not considered a priority for replacement parts. The machine was not repaired and it was subsequently dismantled.
Following World War II, several countries including England, Denmark, France, and Germany tested several windmills in the 100- to 300-kilowatt range. High construction costs and wind unreliability caused these countries to abandon these windmills and dismantle them.
Following the Arab oil embargo of 1973, which caused huge increase in oil prices, the world's attention was focused once more on wind as an alternative source of energy. The advantages of wind energy are that it is renewable, nonpolluting, and free. It is estimated that wind can provide the United States with all its energy needs. The disadvantages of wind energy are that it is diluted, unpredictable, and requires high initial costs. When wind is not blowing, the entire system sits idly by.
In the United States, the Energy Research and Development Administration (ERDA) planned a multi-year wind energy program that was managed by NASA-Lewis Research Center in Cleveland, Ohio. The overall goal of this program was to expedite the development of reliable and cost-competitive wind energy systems that can be used commercially on a significant scale.
The first of the ERDA/NASA program was a 100-kilowatt wind turbine that was installed at NASA's Plum Brook station near Sandusky, Ohio. It became operational in September 1975. Next, four 200-kilowatt wind machines were designed. They were installed at Clayton, N.Mex.; the Island of Culebra, Puerto Rico; Block Island, R.I.; and Kahuka, Hi. These machines started operation in 1979 and 1980.
The next generation of windmills to be tested by NASA were of the megawatt capacity. A 2,000-kilowatt windmill was installed at Boone, N.C. It started operation in 1979.
This was followed by 2,500-kilowatt series of windmills. Three machines were built at Goodnoe Hills in Washington State. They started operation in 1981. In 1982, the Bureau of Reclamation, a part of the United States Department of Interior began testing a 4,000-kilowatt wind machine that was installed near Medicine Bow, Wyo.
All the windmills of the ERDA/NASA's program are of the horizontal-axis type. In addition to the tower and blades, these machines include: (1) A hub which connects the blades to the low-speed shaft. The hub transmits the torque developed by the rotor blades to the shaft and transmits all other blade loads into the bedplate. (2) A pitch-change assembly which consists of a hydraulic supply, a rack and pinion actuator, and gears to rotate the blades in the hub. (3) A drive-train assembly whose purpose is to transmit the mechanical power of the spinning motor to the gearbox. (4) A gearbox that converts the shaft's high-torque low-speed motion into low-torque high-speed motion then fit's the electric generator's requirement. The shaft rotates at 40 rpm while the generator requires 1,800 rpm. (5) A yaw assembly whose function is to support the entire machine assembly on top of the tower and to permit its rotation for alignment with the wind. (6) A generator, whose function is to convert the shaft torque into electricity. This clearly illustrates that converting wind energy directly into electricity is elaborate and requires high initial costs.
The ERDA/NASA's program described above provided valuable information concerning the feasibility of generating electricity from wind. All the windmills in this program were of the horizontal-axis type. However, due to operational problems, all these machines were abandoned and dismantled.
The most successful wind energy program is in the State of California. There are 3 major wind farms at the Altamont Pass, San Gorgonio Pass, and Tehachapi Pass. Their cumulative capacity in 1989 were 634,920 kilowatts, 215,278 kilowatts, and 399,270 kilowatts, respectively. More than 90 percent of the machines are of the horizontal-axis type. The rest are of the vertical-axis type. The windmills of these farms are connected to utility grids.
The windmills currently in use have 2 disadvantages: (1) Each is coupled to its own electric generating equipment. Electric equipment are very expensive and this leads to high initial cost. When wind is not blowing, the entire system sits idly by and (2) The electricity produced by the windmills must be consumed instantly. Typically, wind blows harder by night, when demand on electricity is lowest. This creates operational problem for the utility to whose grid the windmills are connected.
In 1979, Hanley patented an invention (U.S. Pat. No. 4,166,222) in which wind energy is used to produce electricity that is used to lift water from downstream to upstream of a dam with a hydropower plant. The lifted water is stored as potential energy. Upon demand, the water is used to generate electricity.
Hanley's invention addresses the problem of storing wind energy as water potential energy. However, it has the disadvantage of converting wind energy to hydraulic power "which communicate with a power converter 9". Therefore, Hanley's invention, assuming its technical feasibility, involves elaborate equipment and requires high initial costs.